/*-
 * ========================LICENSE_START=================================
 * Smooks Commons
 * %%
 * Copyright (C) 2020 Smooks
 * %%
 * Licensed under the terms of the Apache License Version 2.0, or
 * the GNU Lesser General Public License version 3.0 or later.
 * 
 * SPDX-License-Identifier: Apache-2.0 OR LGPL-3.0-or-later
 * 
 * ======================================================================
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * 
 * ======================================================================
 * 
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 3 of the License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 * =========================LICENSE_END==================================
 */
package org.smooks.thread;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.EmptyStackException;
import java.util.Stack;

/**
 * Stacked ThreadLocal.
 * @author <a href="mailto:tom.fennelly@gmail.com">tom.fennelly@gmail.com</a>
 */
public class StackedThreadLocal<T> {

    private static final Logger LOGGER = LoggerFactory.getLogger(StackedThreadLocal.class);

    private String resourceName;
    private ThreadLocal<Stack<T>> stackTL = new ThreadLocal<Stack<T>>();

    public StackedThreadLocal(String resourceName) {
        this.resourceName = resourceName;
    }

    public T get() {
        Stack<T> execContextStack = getExecutionContextStack();
        try {
            return execContextStack.peek();
        } catch (EmptyStackException e) {
            if(LOGGER.isDebugEnabled()) {
                LOGGER.debug("No currently stacked '" + resourceName + "' instance on active Thread.", e);
            }
            return null;
        }
    }

    public void set(T value) {
        Stack<T> execContextStack = getExecutionContextStack();
        execContextStack.push(value);
    }

    public void remove() {
        Stack<T> execContextStack = getExecutionContextStack();
        try {
            execContextStack.pop();
        } catch (EmptyStackException e) {
            if(LOGGER.isDebugEnabled()) {
                LOGGER.debug("No currently stacked '" + resourceName + "' instance on active Thread.", e);
            }
        }
    }

    private Stack<T> getExecutionContextStack() {
        Stack<T> stack = stackTL.get();
        if(stack == null) {
            synchronized (this) {
                stack = stackTL.get();
                if(stack == null) {
                    stack = new Stack<T>();
                    stackTL.set(stack);
                }
            }
        }
        return stack;
    }
}
